It’s kind of out of date. EnOS ARM was not maintained anymore at one time. The creating images and other maintenance was just too much for one person to maintain.
Since then a new installer Script was created. Calamares was dropped, and the rootfs tar images were dropped, so things are much easier to maintain.
So EnOS is in a kind of Beta trial stage. My guess is It will probably be continued.
The Monitor, keyboard, and mouse are only for an easier installation. You can borrow a Monitor and keyboard, and mouse from your daily driver for about 10 to 15 minutes. Then once the server is installed, all you need is a power supply and Ethernet connection.
You can install the headless server over a SSH connection.
Click on the “download raw file” button open the .odt file with LibreOffice. So one can use a Monitor, Keyboard, and mouse for installation only, or use this tutorial / how to as a learning experience.
The Archlinux ARM repos are a separate entity from the Archlinux x86_64 repos. For 90 % of the packages, they are the same, just compiled for a different architecture.
https://archlinux.org/packages/?sort=&q=plasma&maintainer=&flagged=
Notice under the ‘Arch’ column it says either x86_64 or any.
https://archlinuxarm.org/packages
Notice under the ‘Arch’ column it now says either aarch64 (64 bit) or armv7h (32 bit) or any.
The EndeavourOS specific repo, there are a number of apps that @manuel has created to help users and make things easier. I don’t think the headless server utilizes any of these EnOS app.
Notice there are two repos, x86_64 and aarch64.
I hope that helps. If you have any more questions, let me know.
Pudge
EDIT:
I highly recommend installing the OS on a micro SD card, and have a separate USB 3 SSD for the data. Then go to here and follow tutorials Homeserver 1 thru Homeserver 3 to see how to interface with the headless server using only packages from the Archlinux ARM repos. No 3rd party software. Not real fancy, but it works well.